1. Field of the Invention
The present invention relates to a rubber composition for adhering to steel cords.
2. Description of the Related Art
In order to increase the adhesive force of rubber to steel cords plated with brass, bronze, or zinc, a cobalt salt of an organic acid has heretofore been exclusively used. A technique involving blending of the cobalt salt of an organic acid with a rubber composition to promote the formation of an adhesive interface layer onto steel cords, thus increasing the adhesive force, is known in the art.
In recent years, problems have occurred, such as deterioration in adhesive force caused by high exothermic heat accompanied by higher operating speeds and greater horespower of vehicles, deterioration in adhesive force caused by heat, accompanied by prolonged tire life, or deterioration in adhesive force caused by moisture and heat over a period of time between manufacture and use, thus requiring adhesive properties of a higher level.
Although cobalt is excellent in initial adhesion, heat deterioration (heat aging) causes serious deterioration in adhesive force as described above. Even the use of cobalt can no longer alone satisfy the needs for the high level of adhesion performance required in recent years. It is probable that cobalt is a strong oxidation promoter, and the action thereof to promote the formation of an adhesive layer causes an increase in the thickness of the adhesive layer during travel to lead to fracture of the rubber layer.
Moreover, cobalt is a rare metal, and countries producing the raw material have had problems with political stability. Accordingly, the use of cobalt is disadvantageous because of high fluctuation in price and an unstable supply of rubber products.
The invention has been made under the aforesaid circumstances. An object of the invention is to provide a rubber composition for adhering to steel cords, which has excellent heat-resistant adhesion and moist heat-resistant adhesion, as well as excellent initial adhesion and performance at a level comparable to or higher than that in the related art, as to resistance to rubber fracture.
The rubber composition for adhering to steel cords according to embodiments of the present invention demonstrates excellent adhesion to steel cords. The rubber composition is prepared by adding the following components (A) and (B) to 100 weight parts of a rubber component containing natural rubber and/or a diene synthetic rubber.
(A) A mixture of a compound containing nickel, and a compound containing molybdenum; or a compound containing simultaneously nickel, and molybdenum in a metal-converted amount of 0.01 to 10 weight parts. (B) (b1) 0.2 to 20 weight parts of hexamethylenetetramine or a melamine derivative, and (b2) 0.1 to 10 weight parts of at least one selected from the group consisting of phenol resins, resorcin, resorcin derivatives, and cresol resins.
A composition according to certain embodiments of the present invention is prepared by further adding a compound containing calcium (C) to the foregoing composition.
The composition according to those embodiments of the present invention is prepared by adding the aforesaid compound containing calcium (C) in an amount of 0.1 to 20% in weight ratio to the aforesaid component (A) of the basic composition. Compositions according to still other embodiments of the present invention are prepared by further adding silica (D) to the basic composition or to the calcium-containing composition.
These silica-containing compounds are prepared by adding 1 to 100 weight parts of the aforesaid silica (D) to 100 weight parts of the rubber component of the basic or calcium-containing compositions.
The invention provides a rubber composition for adhering to steel cords which has excellent heat-resistant adhesion and excellent moist heat-resistant adhesion, as well as excellent initial adhesion and performance at a level comparable to or higher than that in the related art, as to resistance to rubber fracture.